Stator vane assembly

Abstract: The inner shroud (48) of the vane of a vane assembly for the compressor section of a gas turbine engine is fabricated from a composite material preferably carbon fibers and imide resin and is formed into an open ended box-like member segment supporting no less than two vanes or airfoils (44,46). The segments are interlocked by a necked down edge adapted to slip into the open end of the adjacent inner shroud of the stator vane that serve to seal the gas path and provide damping. Rub strips (66,68) may be integrally formed on the bottom surface of the inner shroud.

Description: This invention relates to stator vanes for gas turbine engines and particularly to a composite vane and inner shroud. U.S. Patent Number 3,275,294 granted on September 27, 1966 to J. M. Allen and A. J. Scalzo entitled "Elastic Fluid Apparatus" discloses a box-like element on the inner diameter of the stator vane that when assembled define an annular vane construction for a gas turbine engine. The inner shroud or base portions carries interlocking means for interlocking adjacent vanes. The fit of the interlocking means is such that it provides damping. A band formed from relatively thin strip rigidly connects to each of the base members to hold them in frictional engagement relative to each other while permitting radial expansion. The method of bonding the thin strip to the base member is by welding which would require that each of the members are metallic. CH-A-489699 (Gebrüder Sulzer AG) discloses a stator vane assembly comprising a row of spaced stator vanes for passing engine fluid working medium in a gas turbine engine, said assembly comprising a plurality of prefabricated stator segments mounted end to end to form a ring, each segment comprising an outer shroud portion, an inner shroud portion and at least two stator vanes extending between said inner and outer shroud portions; said inner shroud portion being a box-like structure having a top wall joined to the inner end of said stator vanes, a bottom wall, and a pair of opposing parallel side walls, said top wall, said bottom wall and said pair of opposing parallel side walls defining a channel, and means formed on the ends of the channel for interlocking adjacent inner shroud arcuate segments. As is well known in the aeronautical art, it is highly desirable to reduce the weight of engine component parts inasmuch as such a reduction translates into fuel savings and/or greater payload capacity. One area that has proven to lend itself to being fabricated from composite materials is the fan/compressor section of the engine. Since this area during aircraft operations can become relatively warm and encounter extremely high stresses, only certain composite materials have proven to be satisfactory for this environment. One of the materials that have proven to exhibit satisfactory characteristics is the imide resin and carbon fiber family of composite materials. However, because of the characteristics of this material, fabrication of the vane has been particularly difficult. The invention is distinguished over the disclosure of CH-A-489699 in that said stator segments are formed of a composite material and in that said channels in said inner shroud portions are open ended channels aligned to form an annular shaped passageway in said ring. We have found that a vane can be satisfactorily fabricated by forming the vane in segments comprising at least two and perhaps three or more airfoils. In the preferred embodiment, the airfoil section of the vane is fabricated into a solid body with an integral hollow box-like structure formed at the base of the vane to define the inner shroud. The box-like structure carries a pair of opposing side walls a bottom wall and top wall and the ends are void to define an annular cavity when the segments are assembled in a ring like stator vane one end of the hollow box-like element is necked down to fit into the end of the adjacent segment. This construction forms an extremely light weight assembly and doesn't require any additional structural supports as is the case of heretofore known assemblies. Also, circumferential tracks formed from a suitable abradable material may be permanently affixed to the inner diameter of the inner shroud and when assembled mate with the knife edge sealing elements of the labyrinth seal carried by the rotating shaft. Thus the invention may provide a composite stator vane for a gas turbine engine that includes a vane segment that preferably includes at least a pair of circumferentially spaced solid airfoil vanes and an integral hollow box-like inner shroud. The inner shroud defines an annular cavity and includes a necked down end to snugly fit into the end of the adjacent segment and define an interlocking assembly of segments. A further preferred feature of this invention is the provision of circumferentially shaped-rub strips formed on the bottom wall of the inner shroud that are adapted to engage the tooth or teeth of the labyrinth seal formed with the rotating assembly. Another preferred feature of this invention is that the fit between adjacent segments provides sufficient surface contact at the mating joints to perform a damping function. The inner shroud may be either formed independently from the vanes and bonded thereto to form an integral segment, but most preferably, the inner shroud segment and the vane are moulded together as an integral segment. Most preferably, the outer shroud segment is also moulded integrally with the inner shroud segment and vane. Fig. 1 is a partial view in section of a compressor section of a gas turbine engine including vanes utilizing this invention; Fig. 2 is an enlarged side view partly in section of a vane constructed in accordance with this invention; and Fig. 3 is a partial view in section and phantom taken along lines 3-3 of Fig. 2 showing the details of the vane. This invention can best be understood by referring to Figs. 1-3 that show a portion of a compressor section of a gas turbine engine in section generally indicated by reference numeral 10. Compressor casing 11 houses a portion of the compressor stages and for illustration purposes of this invention are shown three compressor rotors 12, 14, and 16, and their complementary stator vane assemblies 18 and 20 (only two being shown). The compressor rotors 12, 14, and 16 comprise the blades 22, 24 and 26 that are circumferentially spaced and supported to or made integral with the respective rotor disks 28, 30 and 32, respectively, in a well known manner. The rotor disks are, in turn, suitably supported to engine shaft 34 by a plurality of nut and bolt assemblies 36 (one being shown) for rotational movement about the engine's axis A. Vane assemblies 18 and 20 consist of a plurality of segments generally indicated by reference numeral 42 that each consist of two vanes or airfoils 44 and 46 extending from an inner shroud 48 to an outer shroud 50. Each of the segments is mounted end to end to form a ring of spaced airfoils surrounding the engine axis A and serve to direct the engine's working medium into the respective compressor blades. For the purpose of this disclosure and for the sake of convenience and simplicity only a single stage of the multiple stages of compressors stages will be described hereinbelow. For this purpose vane assembly 20 has been selected to serve as an example of all the other vane assemblies employing this invention. As mentioned in the above, the stator assembly is fabricated from a non-metal material which consists of a suitable composite material that is capable of withstanding the heat and loads encountered in aircraft engine operation. A suitable material and preferable in this embodiment is a imide resin and carbon fiber composite. While not a part of this invention it should be understood that the fibers are formed in a cloth-like material that is layered to define the stator assembly and then with the use of a suitable adhesive is molded into the desired configuration. It is an important preferred feature of the invention that each segment carries no less than two stator vanes and could carry as many as three or more stator vanes. Each segment includes the box-like inner shroud 48 that consists of an upper wall 52, a bottom wall 54 and opposing front face and back face walls 56 and 58, respectively. The side edges 60 and 62 of the inner shroud 48 are open so that when assembled they define an annular open channel. Side edge 60 of each segment is necked down to a prescribed dimension in order to fit into the open ended channel of the adjacent segment as shown in Fig. 2. The fit of the necked down edge 60 is such that there is a sliding motion between the mating faces that produces sufficient friction to dampen the vibratory motion encountered. This mating of the adjacent segments assures sufficient sealing to prevent leakage of the engine's working medium. The construction of the vane assembly incorporating this invention not only eliminates the need of additional support as the thin band support described in U.S. Patent No. 3,275,294, supra, it also lends itself for supporting the rub strips that are typically employed in gas turbine engines to seal the shaft and its working cavity from the gas path. As shown in all the Figs. rub strips 66 and 68 are integrally molded on the bottom surface of the bottom wall 54 of the inner shroud 48 and define circular sealing elements that engage with the knife edges 70 and 72 extending from the disk support member 73. Since the inner shroud is integral with the vane assembly and no means are necessary for attaching the air foil and shroud assembly, a reduction in weight is realized which contributes to the overall improvement in engine performance. While the inner shroud 48 is configured in a rectangular shape, the construction of the vane assembly incorporating this invention lends itself to be formed in other similar shapes or quasi-like rectangular shapes. This is illustrated in the vane assembly 18 of Fig. 1 which shows the bottom wall to be stepped to accommodate the sealing of an angular shaped disks attachment member. It is to be understood that the term "box-like" as defined in this disclosure, includes configurations that are other than rectangular shaped members as is shown in Fig. 1. It should also be understood that while in its preferred embodiment the inner shroud is molded as a unitary element of the vane assembly, it could be molded as a separate element and bonded to the vanes. What has been described above is a compact and simplified integral vane and inner shroud assembly that includes inherent sealing and damping features, while eliminating the need for the complicated and multi-component support structure that has been typically employed in heretofore known designs. The assembly also includes integral rub strips that may be of the abradable type typically employed in current gas turbine engines. The construction of the vane assembly results in a weight reduction, is easier to assemble and reduces the number of components typically associated with this portion of the gas turbine engine.

Claims: A stator vane assembly (20) comprising a row of spaced stator vanes (44,46) for passing engine fluid working medium in a gas turbine engine, said assembly comprising a plurality of prefabricated stator segments (42) mounted end to end to form a ring, each segment comprising an outer shroud portion (50), an inner shroud portion (48) and at least two stator vanes (44,46) extending between said inner and outer shroud portions; said inner shroud portion being a box-like structure having a top wall (52) joined to the inner end of said stator vanes, a bottom wall (54), and a pair of opposing parallel side walls (56,58), said top wall, said bottom wall and said pair of opposing parallel side walls defining a channel, and means formed on the ends of the channel for interlocking adjacent inner shroud arcuate segments; characterised in that said stator segments are formed of a composite material and in that said channels in said inner shroud portions are open ended channels aligned to form an annular shaped passageway in said ring. A stator as claimed in claim 1 wherein said composite material is taken from the group consisting of carbon fibers and imide resins. A stator as claimed in claim 1 or 2 wherein said interlocking means includes a necked down portion formed on the end of adjacent box-like structures. A stator as claimed in claim 3 wherein said necked down portion fits slidingly into the open ended channel of the adjacent segments, whereby the cooperation of said necked down portion and the open ended channel dampen vibratory energy imposed on said stator. A stator as claimed in any preceding claim including at least one rub strip (66,68) provided on the outer face of said bottom wall and adapted to engage a sealing element attached to the shaft of said gas turbine engine. A stator as claimed in any preceding claim wherein said box-like structure is rectangularly shaped. A stator as claimed in any of claims 1 to 5 wherein said box-like structure is irregularly shaped. A stator as claimed in claim 7 wherein said box-like structure includes a forward portion and an adjoining rearward portion and said forward portion and said rearward portion being in stepped relationship relative to each other. A stator as claimed in any preceding claim wherein each of said at least two stator vanes (44,46) is formed integrally with said inner shroud portion (48). A stator as claimed in any preceding claim, wherein each of said at least two stator vanes (44, 46) is formed integrally with said inner shroud portion (48) and said outer shroud portion (50).

Inventors: MATHENY ALFRED P, NORRIS JAMES W, MATHENY, ALFRED P., NORRIS, JAMES W.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1994
Main classification: F01D9
IPC codes: F01D9, F01D5